<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <title></title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        
        .box {
            width: 500px;
            height: 500px;
            background-image: linear-gradient(to left top, blue, pink);
        }
    </style>
</head>

<body>
    <div class="box"></div>
</body>

</html>